in setdefault printer it mean the printer's real name.
the one you see when you open up printers list in start menu settings (or what ever it is called in english version of windows)

the share name is only for the share (for connecting to share) and the printer name is what the printer is actually called once it's connected.
I know, it's little confusing but...

to make a remote printer default, you not only need to use the name of the printer but you need to use also the server you have connected to.

so:
setdefaultprinter("\\serverName\Printer's name on the server")
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